The present invention relates to a method and device for transmitting data generated by detection and/or measurement means placed in a well.
The present invention is particularly well adapted to measuring while drilling techniques generally designated by the initials MWD.
Well logging during drilling using an MWD type technique are destined for considerable development for two essential reasons; namely, a reduction of well logging costs, and a possibility of remote guiding of the drilling as a function of reservoir objectives which is of particular importance in the case of horizontal drilling. Apart from sensors or detectors for detecting purely drilling parameters, existing tools include a natural gamma radiation measurement probe, possibly oriented, a normal resistivity prove, etc.
There are several method for the transmission of measurements to the surface of the ground; namely, a transmission by cable, a transmission by mud waves, i.e., pressure pulses in drilling mud, and a transmission by electromagnetic waves.
In for example, French Patent No. 1,603,406, 1,603,706, and 1,602,653, several examples of devices for the transmission of data by mud waves are proposed and in, for example, an article entitled "Propagation of Electromagnetic Waves Among the Drilling of a Finite Conductivity" P. DeGauge and R. Gurdjinski, "SPE Drilling Engineering", June 1987, describes a transmission of electromagnetic waves.
While cable transmission has an advantage of being of a very good quality, and operates at high speeds such as, for example, hundreds of measurements per second, a disadvantage thereof resides in the fact that the cable transmission does not generally allow for a rotation of the drill string.
Moreover, while mud or electromagnetic wave transmission does not interfere with the drilling operations, a disadvantage of such transmission resides in the fact that their rate is much slower and amount to about one measurement about every ten seconds.
The achievement of a complete set of MWD well logs could come up against a transmission speed problem in the case of mud wave or electromagnetic wave transmission. This speed would in particular be insufficient in the case where real time processing of the measurements is to be carried out for monitoring the drilling.
The aim underlying the present invention essentially resides in providing a combined transmission which avoids the above mentioned drawbacks and disadvantages by providing combined transmission adapted to give continuously, via mud waves or electromagnetic waves, drilling parameters to which a few measurements related to the geological formation could be added. When the drilling conditions do not need the rotation of the drill string as a whole and when the measurements relative to the generator have an interest (e.g. for guiding drilling), a cable may be connected and enables a denser transmission of data measurements to the surface.
The transmission device of the present invention may also be constructed so that selection of the channels for measurements transmitted by mud waves or electromagnetic waves is normally, and if desired, effected by one of the conductors of the cable. By virtue of the device and method of the present invention make it possible to obtain, with a minimum time lag, pertinent data concerning the drilled geological formations, to reduce the cost of well logging because it is no longer necessary to immobilize the well for long periods of time corresponding to the well logging periods, to obtain a better quality of data since the measurement is achieved very rapidly after drilling, etc. Moreover, the data obtained under these conditions result in a precious saving in time for constructing elements which will be positioned in the well after drilling, such as perforated production casings in which the position of the perforations can be rapidly predicted. By pertinent data should be understood sophisticated data requiring a high transmission flow of the data when it is necessary, e.g. when passing through a critical zone of the geological formation and relatively poor data when the geological formation being drilled has no particular interest. In the case of directed drilling, 25 the poor data transmitted at low frequency may contain in particular the data for directing the drilling and the drilling parameters.
Thus, the present invention relates to a method for transmitting data generated by detection and/or measurement means placed in a well. According to this invention, the transmission is provided from one side by cable, or from another side by mud waves or electromagnetic waves, simultaneously or successively. The transmission may be carried out without withdrawing the detection and/or measurement means from the well. The transmission may be carried out intermittently by cable . The transmission may be carried out during drilling.
When the method of the present invention is applied to drilling by a downhole motor fixed to the end of a drill string, transmission may be made by cable when it is not necessary to rotate the drill string. In this case, transmission by mud waves or electromagnetic waves may be made at least during the drilling periods when cable transmission is not used, or permanently.
The cable may be used to achieve a real time transmission of the data i.e. as soon as the data are available.
The data to be transmitted by cable may equally be stored in a storage member forming part of the lower end 15 of the drill string and the cable may be lowered periodically so as to bring up the data stored in the lower part of the drill string.
The present invention also relates to a device for transmitting data generated by detection and/or measurement means placed in a well, with the device comprising transmission means including a cable and mud wave or electromagnetic wave transmission means, and means for remote connection of the cable with the detection and/or measurement means.
The cable transmission means may include means for storing the data and the detection and/or measurement means may be placed in a drill string substantially in the vicinity of the lower end of this drill string which may include a drilling tool driven by a downhole motor.
When the detection and/or measurement means comprise several channels capable of being transmitted by mud waves or electromagnetic waves, the device of the invention may comprise means for monitoring the channels effectively transmitted, with the monitoring means being adapted for receiving the reference relative to the channels to be transmitted from transmission means including the cable.
The device of the present invention may also comprise a side entry sub, and the cable may be an electric or an optic cable.